1. Field of the Invention
The invention relates to an aluminum nitride substrate for a semiconductor production and/or inspection apparatus, and a production method of the same.
2. Description of the Related Art
Aluminum nitride (AlN), which has a relatively high thermal conductivity about 320 W/mK, is excellent in electric insulation property, mechanical strength, and bondability to metal conductors, so that sintered aluminum nitride bodies obtained by firing aluminum nitride powder have been known as IC substrates or package materials. However, it actually is difficult to obtain a sintered aluminum nitride body having a high thermal conductivity, by firing aluminum nitride powder. Thus, methods for improving thermal conductivity of aluminum nitride have been developed.
One method includes: before firing, densifying AlN particles that have excellent covalent bondability and that are difficult to be sintered, so that the sintered AlN body is improved in thermal conductivity. For example, there is disclosed a method of densifying AlN particles by the addition of a sintering aid (yttria (Y2O3)) in SHO-60 Annual Conference Proceedings of the Ceramic Society of Japan (in 1985, pp. 517-518, by Shinozaki et al.).
Another method includes: adding a substance that is bondable to oxides in a sintered AlN body, and removing oxides therefrom, thereby improving the thermal conductivity of the sintered AlN body. It is supposed that, after such oxidation, the sintered AlN body has resultant voids, which obstruct the transmission of phonons contributing to heat conduction, so that the thermal conductivity is decreased.
For example, Japanese Patent Application Laid-Open Publication No. 60-127267 discloses a method of adding a sintering aid (yttria (Y2O3)), and trapping AlN oxides. Further, Japanese Patent Application Laid-Open Publication No. 61-146769 (counterpart of U.S. Pat. No. 4,578,364 to Huseby et al.) discloses a method of adding carbon for a reaction with oxide, and removing the reaction products.
In turn, Japanese Patent Application Laid-Open Publication No. 9-48668 discloses an AlN ceramic with a sintered AlN body having improved thermal conductivity and strength (page 5, and FIG. 1). Further, Japanese Patent Application Laid-Open Publication No. 2001-223256, which relates to a sintered carbon-containing ceramic body constituting a ceramic substrate for semiconductor production or inspection (page 8, and FIG. 1), discloses rendering the concentration of carbon to be uneven, so that an electrode pattern is prevented from being seen through the ceramic substrate, while adjusting the volume resistivity of ceramic substrate.
If the thermal conductivity of the AlN sintered body is improved by adding an amount of particles of carbon (hereafter sometimes simply called “carbon”) to AlN powder in a conventional manner, the sintered AlN body tends to have an irregular-colored appearance, and suffers from varieties of problems with product quality. Particularly, the adoption of AlN powder including excessive carbon leads to complicated firing so that the crystal grains in the sintered AlN body tend to be separated, thereby deteriorating the quality of the ceramic substrate. Further, when excessively added carbon is left partially unreacted in the sintered AlN body, the densification of the sintered AlN body is obstructed, which cause deterioration in the thermal conductivity of the sintered AlN body. In this respect, although the Japanese Patent Publication No. 60-127267 has added carbon in an amount sufficient to stoichiometrically react with the oxygen (oxides) contained in the AlN powder, the mere optimization of the amount of carbon fails to produce a sintered AlN body having a high thermal conductivity.
Further, although the Japanese Patent Application Laid-Open Publication No. 2001-223256 achieved a non-uniform carbon concentration in the ceramic substrate, it is impossible to control the existence form of carbon, and carbon that is possibly present in a grain boundary of the sintered AlN body tends to cause grain separation, thereby resulting in deteriorated quality.